Method for working normally-brittle sheet metal



W. E. RUDER April 14,1931.

METHOD FOR WORKING NORMALLY BRITTLE SHEET METAL Filed May 8, 1928 Inventor: William E.RLJC1e F,

His Attorney.

Patented Apr. 14, 1931 f UNITED STATES PATENT OFl-ICE WILLIAII E; RUDER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC GOMPAENY, A CORPORATION OF NEW YORK METHOD FOR WORKING NORMALLY-IBRITTLE' SHEET METAL Application filed May 8, 1928. Serial No. 278,175.

mium. A small amount of carbon preferably less than one tenth per cent and less than one per cent each of silicon and manganese ma be present in the alloy. The alloy usua y contains the above metals in the following percentages by weight:

Aluminum 46% Chromium 12-15% Carbon less than-.10% Silicon a less than 1% Manganese less than 1% Iron remainder I These proportions may bevaried somewhat depending upon the properties desired in the alloy. For example, the aluminum content a0 tent as low as 10%. l

- The alloy containing the above ingredients has very desirable mechanical and electricalproperties and in addltionus comparatively inexpensive. These qualifications .render it particularly suitable for use as a resistor element in control rheostats. In manufacturing'such rheostats the alloy is rolled into thin flat strips which are subjected to a shearing operation to produce a narrow thin metal ribbon which is wound edgewise into a coil to provide the resistor element of the rheostat The shear ng operation apparently produces .a certalndegree of brittleness in the material, so that when wound into a coil having substantially rectangular form considerable difliculty has been encountered due to the tendency ofthe :material to break or fracture at the points 30 }where it is bent sharply at right, angles to may be as low as 2% and the chromium c011 itself. It is one of the objects of the present invention to provide means whereby this difliculty may be avoided.

Thenovel features which I believe to be characteristic of 'the invention are set forth with particularity in the appended claims. The invention itself however will-best be understood from reference to the following specification when considered in connection with the accompanying drawing in which, the single figure .shows diagrammatically a perspective view of an apparatus whereby'the invention may be carried into effect.

Referring more-particularly to the drawing, I have indicated at 1 a bending machine comprising a hardened steel bending die 2 which is carried by a solid steel wheel 3, the latter being driven from a source of power through a pulley l and belt 5. The alloy conductor comprises a relatively thin flat ribbon 6 which may be wound upon a wheel 7 and fed to the die 2 through an electrical heating coil 8 supplied from a source of energy not shown. The wheel 3 and die 2 are heated by a plurality of blow torches 9 or any other suitable means.

Coil 8 and blow torches 9 warm the alloy conductor 6 and die 2 to a temperature which is well below 200 C. but at which the conductor may be bent without danger of fracture. I have found that a temperature above 80 and in the neighborhood of 100 will give uniformly satisfactory results. (Vhlle .the temperature may vary considerably, it-

should be well above room temperature and well below 200 C. The latter temperature should not be exceeded, since the hardened steel bending die will become progressively softened about this temperature and soon become useless.

After the process has been in operation for some time the heat supplied by coil 8 maybe increased slightly and the heating of the wheel 3 and die 2 by means of blow torches discon- 9r tinued. It will be found that the heat supplied by the coil 8 after the process has been in operation for some time is suflicient to keep the die 2 warm enough so that the ribbon conductor may be bent into the desired form without causing any break or fracture in the material.

What I'claim as new and desire to secure by Letters Patent of the United States is:

1. The method of winding a flat metallic conductor edgewise into a coil, which comprises heating the conductor to a temperature well above room temperature and well below 200 C. and then winding it on a die warmed to approximately the same temperature as the conductor.

2. The method of winding a flat normally brittle electrical conductor edgewise into a coil, which comprises heating the conductor and winding it on a heated die, the temperature of the conductor and die being below 200 C. but high enough to prevent fracture of the material when bent into a rectangular-- shaped coil.

3. The method of producing sharp bends in sheet metal whichconsists largely of iron but contains appreciable amounts of chromium and aluminum, which comprises heating the metal to a temperature above room temperature and well below 200 C. and then bending it on a die having approximately the same temperature as the conductor.

4. The method of making resistance grids from strip material composed of an ironchromium-aluminum alloy in which the chromium content ranges from about 10% to about 15%, the aluminum content from about 2% to about 6% with the remainder iron except for incidental impurities, which consists in heating the strip to a temperature well above room temperature but below 200 (1., and then bending it edgewise on a die warmed to a temperature below 200 C. but wellabove room temperature.

In witness whereof, I have hereunto set my hand this7th day of May, 1928.

' -WILLIAM E. .RUDER. 

